WO1995022643A1

WO1995022643A1 - Method of growing single crystal

Info

Publication number: WO1995022643A1
Application number: PCT/JP1994/002089
Authority: WO
Inventors: Yoshiteru Taniguchi; Toshiaki Asahi
Original assignee: Japan Energy Corporation
Priority date: 1994-02-21
Filing date: 1994-12-14
Publication date: 1995-08-24
Also published as: US5603763A; JP3232461B2

Abstract

A method of growing a single crystal for producing a compound semiconductor single crystal having a high quality and a large diameter in a high yield. An easily volatile element (2) is put into a reservoir portion (1A) of a quartz ampule (1) and a crucible (4) made of pBN, into which a compound semiconductor starting material (3A) is charged, is vacuum-sealed into the quartz ampule (1). While vapor pressure control is being made, cooling is gradually made by conducting temperature distribution control so that a first temperature gradient (α°C/cm) in a vertical direction at that portion in the proximity of the outer wall of the quartz ampule (1) corresponding to a molten solution (3B) of the starting material is smaller than a second temperature gradient (β°C/cm) in the vertical direction at a portion above the upper end of the crucible (4). Here, α is 51/D2 to 102/D2 and preferably, 58/D2 to 83/D2°C/cm (D (cm): diameter of single crystal), and β is 1.06X to 1.72X and preferably, 1.19X to 1.46X°C/cm (X = X(Rς/μnL) where cooling rate of furnace internal temperature is R°C/hr, and heat transfer rate, specific gravity, molten latent heat and formula weight of crystal are μkcal/cm.hr.K, ςg/cm3, L.kcal/mol and ng/mol, respectively.

Description

Single crystal growth method Technical field

The present invention relates to a method for growing a single crystal of a compound semiconductor, and in particular, to grow a single crystal such as CdZnTe or CdTe by melt growth by vertical gradient freezing (VGF) while controlling the vapor pressure. About the method. Background art

Conventionally, as a method for growing a single crystal of a compound semiconductor, a vertical gradient freezing (VGF) method, a vertical prism man method, and the like have been known. An application has been filed for a method for controlling various growth conditions in order to grow a high-quality single crystal having few dislocations and the like.

For example, regarding the VGF method, the invention described in Japanese Patent Publication No. 5-59873 filed by the present applicant has been known. The content of the invention is that the temperature distribution in the heating furnace is maintained at 0.1 to 10 while maintaining the temperature distribution such that the center of the surface of the raw material melt is lowest, becomes higher toward the outside in the radial direction, and becomes higher toward the bottom. This is to cool the inside of the heating furnace at a solid-liquid interface temperature gradient of 'CZcin and a cooling rate of 0.01 to 1' CZhr, and grow a single crystal downward from the center of the melt surface.

In the vertical Bridgeman method, a method of adjusting a furnace wall temperature gradient along a crystal and a furnace wall temperature gradient along a melt based on the thermal conductivity between the crystal and the melt (Japanese Patent Laid-Open No. 2-239181). And the method of detecting and controlling the temperature at multiple locations on the outer periphery of the crucible and calculating and estimating the temperature distribution inside the crucible and the position and shape of the growth interface at regular intervals based on the temperature. (Described in Japanese Patent Application Laid-Open No. Hei 1-212291).

In addition to the above-mentioned prior application, a method of growing a crystal by using a vertical heating furnace and providing a vertical temperature gradient, such as the VGF method or the vertical Bridgeman method, is disclosed in Japanese Patent Application Laid-Open No. The inventions of JP-A-3-183682 are known. JP 20 -The invention of No. 1 6 7 8 8 2 uses a vertical container having a substantially inverted conical part at the top and a small opening at the top, and fills the container with the raw material melt and melts the raw material. The raw material melt is solidified downward by bringing the seed crystal into contact with the liquid through the upper small opening. The invention of Japanese Patent Application Laid-Open No. 3-186382 is an improved version of the invention of Japanese Patent Application Laid-Open No. 2-168782, which is different from the one used in Japanese Patent Application Laid-Open No. 2-168782. A lower small opening is provided at the lower part of the same vertical container to allow the excess raw material melt to flow out, and the raw material melt flows out from the lower small opening to damage the container due to volume expansion accompanying solidification of the raw material melt, etc. Is to be avoided.

Also, in a method using a horizontal heating furnace such as a horizontal bridgeman method or a horizontal gradient freezing method, the invention described in JP-B-53-56867 is known. This is because the vessel containing the melt and the seed (seed crystal) is placed in a horizontal furnace, and the temperature of the surface of the melt that contacts the bottom of the vessel is always higher than the temperature of the free (ie, upper) surface of the melt. By holding it high, the melt solidifies so that it starts at the top and ends at the bottom of the container.

However, according to the control method described in Japanese Patent Publication No. 5-589873, a single crystal of higher quality than the vertical Pledgeman method can be obtained, but all the grown crystals (ingots) can be obtained. ) Is not always a single crystal, and there is a problem that the yield is not so high due to polycrystallization.

In recent years, a single crystal having a small diameter and good quality (for example, 4 inches in diameter) with less crystal defects such as dislocations has been desired. However, a method for producing such a single crystal with a high yield is still required. Has not been established.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for growing a single crystal which is superior in quality and which can produce a large-diameter single crystal with high yield. Is to do. Disclosure of the invention

In order to achieve the above object, the present inventors first put a CdZnTe raw material into a pBN (pyrolytic boron nitride) wrapper, vacuum-enclose it in a quartz ampoule, 3 inch (diameter) crystal of CdZnTe is grown by the The obtained number of rectangular substrates of 25 ππι Χ 3 π ππ that passed the product standard was evaluated as the average value per single growth (yield of single crystal substrate).

As a result, without controlling the vapor pressure (however, a simple substance of Cd in an amount corresponding to the internal volume was placed in the quartz ampoule together with the above-mentioned raw materials), as shown in Fig. 1 (a). When a two-stage heating furnace 10 having two-stage heaters 11 and 12 was used, the yield of single crystal substrates was 4.6 to 4.8, whereas quartz with a reservoir part was used. Using an ampoule, the three-stage heater 21, 22, 22, as shown in Fig. 1 (b), while performing vapor pressure control to uniformly heat and hold the reservoir containing the Cd alone When a three-stage heating furnace 20 having 23 was used, the yield was improved to 10.9 sheets.

The present inventors focused on the fact that there were a furnace with a good yield of a single crystal substrate and a furnace with a bad single crystal substrate in the case of a three-stage heating furnace in which such a vapor pressure control was performed, and examined the causes. We found that there was a difference in the temperature distribution inside the furnace between a good furnace and a bad furnace. Then, from the temperature distribution in the furnace of the three-stage heating furnace with good performance, the first temperature gradient in the vertical direction near the outer wall of the quartz sample corresponding to the raw material melt and the upper side of the upper end of the loop. Then, the present inventors have found an appropriate range for the second temperature gradient in the vertical direction in the furnace. In order to control the temperature distribution, a 7-stage heater with a 7-stage heater 31, 32, 33, 34, 35, 36 A, 36 B as shown in Fig. 1 (c) When a single crystal was grown using the mold heating furnace 30, an excellent result was obtained in which the yield of single crystal substrates was 21.6. By improving the furnace temperature distribution of the three-stage heating furnace 20 based on the furnace temperature distribution in the seven-stage heating furnace 30 and by avoiding the use of a furnace that cannot be improved, the three-stage heating furnace However, the yield of single crystal substrates could be improved to 20 substrates. Therefore, it was confirmed that it is important to keep the first temperature gradient and the second temperature gradient within appropriate ranges, respectively, in order to increase the yield of the single crystal substrate.

Furthermore, the present inventors attempted to grow a single crystal by increasing the diameter of the crystal to be grown to 4 inches, and found that the first temperature gradient was larger than that in the case where the diameter of the crystal was 3 inches. Was found to be smaller. Based on this knowledge, the value of the appropriate range of the first temperature gradient was converted into a relational expression using the diameter of the single crystal as a parameter, The present invention has been completed by performing a heat calculation and generalizing the value in the appropriate range of the second temperature gradient.

That is, the method for growing a single crystal according to the present invention includes the steps of: adding a simple substance or a compound made of at least one kind of volatile element among the constituent elements of the compound semiconductor into the reservoir part of the quartz ampule having the reservoir part; After placing a pBN crucible containing the compound semiconductor material in the quartz ampoule and vacuum-sealing the quartz sample, the quartz amble is heated in a heating furnace to melt the material. The reservoir is heated to a predetermined temperature, and the vapor pressure of the element, which is easily volatilized in the reservoir, is controlled by applying the vapor pressure in the quartz amble, and the outer wall of the quartz tumbler corresponding to the molten raw material melt is controlled. A first temperature gradient in the vicinity in the vertical direction (a: / cm) is higher than the upper end of the crucible (in this specification, the range from the upper end of the crucible to the upper side of l Ocn is defined as The temperature in the heating furnace is gradually controlled while controlling the temperature distribution in the heating furnace so as to be smaller than the second temperature gradient in the vertical direction at (/ 9 / cm). When the single crystal of the compound semiconductor is grown downward from the surface of the raw material melt and the diameter of the single crystal to be grown is Dcm, the first temperature gradient (a ′) (CZcm) is 51 / D2 to 102 / D2'CZcm, more preferably 58 ZD2 to 83ZD2'C / cn.On the other hand, the cooling rate at the furnace temperature is controlled by the thermal conductivity of the R'C / hr crystal.

When the specific gravity of the crystal is P gZcm ³ , the latent heat of fusion of the crystal is Lkcal / nol, and the formula weight of the crystal is ng / nol, the following formula:

X = (R / λ n L)

The second temperature gradient (/ S'CZcn) is 1.06 to 1.72X'C / cm, more preferably 1.19X to 1.46X'C. / cm. Note that there is a transition region between the first temperature gradient (a'C / cni) and the second temperature gradient (/ cm).

Specifically, for example, as the heating furnace, at least a first heating means disposed at a position corresponding to the crucible to control the first temperature gradient (a'CZcn); A second heating means arranged above the first heating means for controlling the second temperature gradient (/ S'C / cn); and a second heating means arranged below the first heating means. Third heating means for heating the reservoir portion; and a third heating means above the second heating means and the third heating means. A fourth heating means disposed below the heating means for suppressing the influence of disturbance on the first temperature gradient (a'CZcia) and the second temperature gradient (/ S'C / cn); And a sixth heating means disposed between the first heating means and the third heating means for suppressing mutual effects between the first heating means and the third heating means. Use a heating furnace with a heating means of And, for example, the single crystal of the compound semiconductor is CdZnTe or CdTe, and the temperature of the reservoir at that time is preferably 770 to 830'C, more preferably 790 to 820'C. It is.

Here, the value of the first temperature gradient (a'CZcm) is within the above range for the following reason. That is, in the method of growing a single crystal from the melt surface, the nuclei generated on the melt surface during the process of lowering the furnace temperature grow into a single crystal, but the first temperature gradient (α-C / (cm) is too large, the convection of the melt becomes strong, and nuclei generated on the melt surface are lost due to convection. It becomes impossible to keep the temperature of the side wall lower than the melting point. If nucleation is destabilized or if the temperature of the side wall falls below the melting point, polycrystallization is very likely to occur, which is not preferable for growing a single crystal.

The value of the second temperature gradient (/ S'C / cni) is in the above range for the following reason. That is, if the second temperature gradient (/ 9'CZcn) is too small, the amount of heat absorbed from the surface of the melt or the upper part of the crystal becomes smaller than the amount of heat due to the latent heat of fusion of the crystal, and the crystal becomes polycrystalline. This is because the temperature of the inner wall of the crucible on the melt surface becomes lower than the melting point at an early stage of crystal growth, and polycrystallizes from there.

Furthermore, according to the experiments performed by the present inventors, the temperature of the reservoir was 770 when the single crystal of CdZnTe or CdTe was grown within the above range. At ~ 83 O'C, the maximum diameter of the precipitate in the grown crystal is about 1 O ^ m, and at 790 ~ 820'C, the maximum diameter does not reach 5 m. (See Fig. 4).

According to the single crystal growth method of the present invention, since the single crystal is grown while controlling the temperature distribution in the heating furnace so that a <8 as described above, the amount of heat radiation from the melt surface is large. The growth of the single crystal starts downward from the melt surface, and the single crystal During the growth, the temperature of the inner circumference of the ruffle is maintained at a temperature equal to or higher than the melting point of the raw material melt, so that the single crystal grown from the melt surface is suspended on the melt. This prevents the growing single crystal from coming into contact with the inner wall of the ruffle to generate new nuclei there and polycrystallize, thereby producing a large-diameter single crystal with a high yield.

In addition, using a quartz ampoule with a reservoir, the reservoir containing a simple substance or a compound containing at least one volatile element (at least one of the constituent elements of the compound semiconductor) is heated to a predetermined temperature. The vapor pressure is controlled by applying the vapor pressure of the volatile element, so that it is applied compared to the case where a predetermined amount of the volatile element is simply put in a quartz gamble without a reservoir. In addition to suppressing variations in vapor pressure, decomposition on the grown single crystal surface and evaporation from the raw material melt are more effectively suppressed, reducing lineage and generating large precipitates. Is prevented, and a higher quality single crystal is obtained.

In addition, a PBN crucible was used in a quartz ampoule as a growth vessel in a vacuum sealed container.However, a PBN crucible has an anisotropy in which the thermal conductivity on the side walls is high in the vertical direction and low in the horizontal direction. Therefore, the amount of heat applied to the lower part of the crucible is easily transferred to the upper part of the crucible side wall, and the amount of heat dissipated in the horizontal direction is kept small. It is extremely effective in keeping the melting point or higher. Needless to say, the pBN rupple also has an effect of preventing contamination of impurities. In addition, the crucible is provided with a draft (taper) for removing the crystal after growth, so that the crystal is easily pulled out.

Furthermore, assuming that the diameter of the single crystal to be grown is Den, the first temperature gradient (n ^ / οπι) in the vertical direction near the outer wall of the stone ampoule corresponding to the raw material melt is 51 / D2 ~. 10 2 / D2'C / cnix, more preferably 58 / D2-83ZZD2'C / ca, so the first temperature gradient (CZCB) is not too large and the surface of the melt The convection of the melt does not become strong enough to eliminate the nuclei generated in the first step, so that the nucleation is stabilized, while the first temperature gradient (a'C / cm) is not too small and Since the amount of heat supplied to the crucible is kept at an appropriate level, the crucible side walls are maintained at a temperature equal to or higher than the melting point during the growth of the single crystal, and a large-diameter single crystal is produced with high yield.

In particular, as a heating furnace, a multistage having at least the first to sixth heating means described above is used. By using a mold furnace, the controllability of the first temperature gradient (cr'CZcn) and the second temperature gradient (• CZcn) is extremely improved, and the yield of the single crystal substrate is dramatically improved. Further, when growing a single crystal of CdZnTe or CdTe, if the temperature of the reservoir is 770 to 830, the precipitate in the grown crystal has a diameter of at most 10%. If it is as small as about m, and if it is between 790 and 820, the precipitates are extremely small, not exceeding a diameter of 5 #m at the maximum, and therefore a single crystal of extremely excellent quality can be obtained. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic cross-sectional view schematically showing a three-type heating furnace used in the VGF method. FIG. 2 is a schematic cross-sectional view of a three-stage heating furnace used in the present embodiment. FIG. 4 is a temperature location characteristic diagram showing an example of a raw material melt and a furnace temperature distribution above the raw material melt in the present embodiment. FIG. 4 is a correlation between a reservoir temperature and a precipitate diameter in the present embodiment. FIG. 4 is a characteristic diagram illustrating a relationship. BEST MODE FOR CARRYING OUT THE INVENTION

The method for growing a single crystal according to the present invention is characterized in that, while performing vapor pressure control by heating and holding a reservoir portion of a quartz ampule to a predetermined temperature, a vertical Temperature distribution in the furnace so that the first temperature gradient (a'C / cn) is smaller than the second vertical temperature gradient above the top of the crucible (/ 9'C / cm) A single crystal of the compound semiconductor is grown downward from the surface of the raw material melt while controlling, and the first temperature gradient (a'C / cm) and the second temperature gradient (/ S ° C / cni), each of which specifies the appropriate range.First, the process of defining each of these appropriate ranges will be described, whereby the present invention has been completed based on objective facts. It is a universal one that is not restricted by the diameter or composition of the single crystal to be grown. The basis of it.

First, the present inventors used a plurality of heating furnaces having the same configuration as the three-stage heating furnace 20 shown in FIG. 1 (b) and used a CdZnTe single crystal having a diameter of 8 ODD (3 inches). (Experiment 1), the temperature distribution characteristics of the furnace in a furnace with good yield and a furnace with a poor yield of single crystal substrate A comparison was made. The furnace temperature distribution was examined for the case where the grown crystal was a single crystal and for the case where the crystal was a polycrystal. As a result, the first temperature gradient (a'C / cia) when a single crystal was obtained was obtained. Is in the range of 0.8 to 1.6'C / CBK, more preferably 0.9 to 1.3C / CB, while the second temperature gradient (/ S'CZcm) is 1.6. It was found to be ~ 2.6 "C / cm, more preferably 1.8-2.2cm / cm.

In this experiment 1, as shown in FIG. 2, a quartz sample 1 having a reservoir portion 1A was used, and a volatile element Cd simple substance 2 was put in the reservoir portion 1A. The dZnTe raw material 3A was placed in a PBN loop 4 and placed in the quartz sample 1, and then the quartz ampule 1 was vacuum-sealed. Then, the raw material 3A in the heating pipe 4 is melted by the heater 22 and the reservoir 1A is heated to a predetermined temperature, for example, 770 to 83O'C by the heater 23 to control the vapor pressure. At the same time, the lower part of the top 4 of the heater 21 was heated. While controlling the amount of electric power supplied to the heaters 21, 22, and 23 by a control device (not shown) so that a desired temperature distribution is generated in the heating furnace 20, the temperature in the heating furnace 20 is gradually lowered to melt the raw material. Liquid 3B was crystallized downward from the surface.

Thermocouples 5A, 5B, 5C, 5D, and 5E were installed near the outer wall of quartz amble 1, and the temperature near the outer wall of quartz amble 1 was measured. The values of the thermocouples 5 A, 5 B, 5 C, 5 D, and 5 E are the bottom of quartz amble 1, 3 Οπ π above the bottom, 6 Οη π above the bottom, 9 Οη π above the bottom, and the quartz amble 1 These are the locations corresponding to the cap 1 Β (22 Οηιπ above the bottom). Based on the temperature measured by these five thermocouples 5Α, 5Β, 5C, 5D, 5Ε, the first temperature gradient (a'C / cm) and the second temperature gradient (/ S'C / cni) was determined.

By the way, the present inventors have proposed that the first temperature gradient (α / cm) and the second temperature gradient (/ 3 * CZcin) be accurately set within the appropriate range described above. As shown in Fig. 1 (c), a 7-stage heating furnace 30 having a configuration having 7 stages of heaters 31, 32, 33, 34, 35, 36A, and 36B was prototyped. When the single-crystal growth was performed in the seven-stage heating furnace 30 using a plurality of thermocouples in the same manner as in the three-stage heating furnace 20, the temperature distribution in the furnace was examined (Experiment 2). The temperature gradient from the surface of the raw material melt, that is, the first temperature gradient (a'CZcm) is almost constant from the start to the end of growth. It was found that the accuracy of temperature control was improved as compared with the three-stage heating furnace 20.

In FIG. 1 (c), a heater 31 is a first heating means disposed at a position corresponding to the ramp to control the first temperature gradient, and a heater 32 is located above the ramp. This is a second heating means for heating the space above the end to control the second temperature gradient, and a heater 33 is a third heating means for heating the reservoir section 1A. , 35 are fourth heating means and fifth heating means for suppressing the influence of disturbance on the furnace temperature distribution, and heaters 36A and 36B suppress mutual influence between the heater 31 and the heater 33. This is the sixth heating means. The sixth heating means may have one heater, and the number of heaters is not limited to seven and may be eight or more.

Next, the present inventors tried to grow a 4-inch diameter CdZnTe single crystal using the above-described seven-stage heating furnace 30 in the same manner as in Experiment 1 (Experiment 3). ), a first temperature gradient ((X 'CZCB) is 0.53' second temperature gradient C CB (/ S'CZcm) were single crystals were obtained under the conditions of 1. 83 ^e C / cm From this, it can be seen that as the diameter of the crystal to be grown becomes larger, the appropriate value of the first temperature gradient (a'C / cm) becomes smaller, and the first temperature gradient (a'CZcm) becomes the cross-sectional area of the crystal ( In other words, in this experiment, the vapor pressure was controlled by heating the reservoir 1A by the heater 33 to a predetermined temperature, for example, 770 to 830. Based on the above findings, considering the allowable range of temperature fluctuation due to various factors, etc., the appropriate range of the first temperature gradient (a'C / cn) was Assuming that the diameter is D cm, 51 ZD2 ~ 102 / D2'C / c, more preferably 58/83 ZD2, C / cm.

FIG. 3 shows a temperature-in-position characteristic diagram of an example of the furnace temperature distribution when a single crystal having a diameter of 4 inches was obtained. In FIG. 3, each block is a temperature measured by a thermocouple.

Next, the present inventors set the preconditions for estimating the temperature gradient at the solid-liquid interface, which can be determined from the temperatures of the single crystal, the raw material melt, and the inner wall of the rupee, which cannot be measured during actual crystal growth. And the following calculation was performed. The precondition is that The amount of heat Q1 that transfers heat in the crystallized single crystal is equal to the latent heat of fusion Q2 of the raw material melt (Ql = Q2), and the following numerical values and symbols were used in the calculation.

Cooling rate of furnace temperature: 0.1 l KZhr

Single crystal diameter: 100BB (4 inches)

Thermal conductivity of C d Te (value near melting point): 1.

1.2 kcal / «-hr-K

Specific gravity of C d Te: 5.86 / «iol

Latent heat of fusion of C d Te: 12 kcal / inol

Temperature gradient at solid-liquid interface: XK / CB

The amount of heat Q1 that transfers heat in the grown and solidified single crystal is expressed by the following equation.

Ql = ^ X 52 (cm2) X X (K / cni) X I. 29 (kcal / n-hr

= 1. 0 1 3 Χ (kcal / hr)

The latent heat of fusion Q2 of the raw material melt is given by the following equation.

Q2 = 0.1 (K / hr) ÷ X (K / CB) π π Χ5 ^ (cm2) X5.86 (g / cn3

)

÷ 240 (g / nol) X 1 2 (kcal / nol)

= 2.301 / X (kcal / hr)

Since Q 1 = Q2,

1.01 3 X = 2.30 1 / X

And solving this equation,

Is obtained. In other words, it is estimated that the temperature gradient at the solid-liquid interface is 1.51 K / ca.From the above, it can be seen that the quartz ampoule, like the growth of the 4-inch diameter CdZnTe single crystal described above, Even if the temperature gradient (a'CZcm) measured near the outer wall is smaller than 1. O KZcm, the temperature gradient at the actual single crystal or solid-liquid interface is larger than that. It can be seen that the temperature is slightly lower than the temperature gradient (1.83K / cn) in the space above the upper end. Therefore, based on the precondition that the amount of heat Q1 that transfers heat in the grown and solidified single crystal is equal to the latent heat of fusion Q2 of the raw material melt, As will be described later, the second temperature gradient (/ 9'C / cni) can be generalized. In addition, since the temperature gradient at the actual single crystal or solid-liquid interface is 1.51 K / CB, the growth rate of the single crystal is estimated to be 0.66 inin hr by the following formula.

0.1 (K / hr) ÷ 1.5 1 (K / cn) = 0.66 (nm / hr)

Therefore, for example, the actual growth time of a single crystal having a length of 6 mm is 91 hours according to the following formula.

60 (ππ) ÷ 0.66 (nnZhr) = 9 1 (hr)

Usually, the temperature of the outer wall of the quartz sample at the position corresponding to the surface of the raw material melt at the start of growth is 1117, and from that temperature, the quartz ampoule is cooled at a cooling rate of 0.1 Khr. When the temperature of the outer wall reaches the melting point of the raw material melt (1098), single crystal growth has been completely completed. Here, if the temperature difference between the inner wall of the crucible and the outer wall of the quartz ampoule is estimated to be 5 K (a value obtained from a preliminary experiment conducted by inserting a thermocouple into the raw material melt), the temperature of the outer wall of the quartz amble becomes As of 1 103, single crystal growth has already been completed. Therefore, the actual growth time is 91 hours out of 140 hours from 111 to 113'C, and the temperature of the quartz ampoule outer wall is 1 1 1 2 after 49 hours from the start of growth. When this happens, growth nuclei are generated on the surface of the raw material melt. From this, it can be seen that a single crystal can be obtained if the temperature distribution in the furnace is controlled with good accuracy until several tens of hours or about 100 hours after the start of growth.

Next, the present inventors can apply the present invention also to single crystal growth of other compound semiconductors such as InP, GaAs, ZnSe, and ZnTe other than CdTe. To make it easier, the second temperature gradient (/ S'CZcn) was generalized based on the results of the thermal calculations performed in the specific example described above. The prerequisite at this time is the same as in the above specific example, and the heat quantity Q1 for transferring heat in the grown and solidified single crystal is equal to the latent heat of fusion Q2 of the raw material melt (Q1 = Q2). The numerical values of the preconditions such as the cooling rate of the furnace temperature are symbolized as follows.

Cooling rate of furnace temperature (KZhr): R

Cross section of single crystal (cni2): S

Thermal conductivity of crystal (kcalZcurhr'K): λ Specific gravity of crystal (gZcB ³ ): P

Latent heat of fusion of crystal (kcalZno!): L

Temperature gradient at solid-liquid interface (KZCB): X

Formula weight of crystal (gZBol): n

The amount of heat Q1 transferred in the grown and solidified single crystal is expressed by the following equation.

Q1 = S XXX λ

Q2 = R ÷ XX S X p ÷ n XL

Since Q 1 = Q2,

SXXX A = R ÷ XX SX ÷ n X L

And solving this equation for X gives

X = (R Ρ / λ n L)

Is obtained.

Based on this, considering the allowable range of temperature fluctuation due to various factors, the appropriate range of the second temperature gradient (S'C / cn) is 1.06 X to 1.72 X ° CZcm, It is preferably 1.19 X ~ 1.46 X'C / cn.

As described above, in order to verify the validity of generalizing the first temperature gradient (α / cm) and the second temperature gradient (β • C / cn), (A'C cm) and the second temperature gradient (S'C / CB) were set to values selected from the generalized appropriate range, respectively, and C d Z The nTe single crystal was grown several times (Experiment 4). The plane orientation of the obtained single crystal was always the (111) plane which was the preferred growth direction. When the substrate cut out of the single crystal was etched with an HF-based etchant and the etch-pit density (EPD) was measured, the EPD was found to be 4 X 104 to 6 X 104 _C in-2. there were. This value is equivalent to the dislocation density (K. Nakasawa et al., Appl. Phys. Lett., 34 (1 979) 574). Furthermore, the half value width of the diffraction line by the (333) plane in the four crystal X-ray diffraction measurement was 20 seconds or less (7 to 20 seconds). From these measurement results, it was found that the obtained CdZnTe single crystal had good crystallinity, and the validity of the present invention was confirmed. Subsequently, the present inventors conducted experiments to define the optimum range of the temperature of the reservoir 1 A, which is a factor that determines the magnitude of the vapor pressure of the volatile element to be subjected to vapor pressure control. (Experiment 5). The results are shown in Fig. 4, which shows that if the temperature of the reservoir 1A is 770 to 830, that is, the vapor pressure of Cd is approximately 1.0 to 2.0 atm, The precipitate has a diameter of at most 10; m at the maximum, and if the vapor pressure of Cd is 790 to 820, that is, if the vapor pressure of Cd is approximately 1.3 to 1.8 atm, the precipitate is at most a diameter. Since it is estimated that the temperature is extremely small, not reaching 5, it was found that the temperature of the reservoir section 1A is preferably 770 to 830, more preferably 790 to 820. When the temperature of the reservoir 1A is about 813 (approximately 815 to 825 ° C) and the vapor pressure of Cd is 1.7 atm, the electric conduction type of the crystal becomes a P-type and n-type inversion region. The precipitate was the smallest.

In Experiment 5, the reservoir section 1A was heated to 780 ° C, about 813 ° C, and 850 ° C at 750 ° C. A crystal was grown. Then, the size of the precipitate in the obtained single crystal was measured by an infrared microscope.

Therefore, according to the present invention, even when a seven-stage heating furnace as described above is used as the heating furnace, and even when a three-stage heating furnace is used, a single crystal having a larger diameter and a larger diameter can be produced with higher quality. Can be manufactured well.

It should be noted that the present invention is not at all limited by the above-described embodiment, and examples thereof include, for example, InP, GaAs, 2nSe, and ZnTe other than CdTe and CdZnTe. It is also applicable to single crystal growth of other compound semiconductors, and the diameter of the single crystal to be grown is not limited to 3 inches or 4 inches. Not limited to 7 steps.

In addition, as in the above embodiment, single crystal growth was performed while always measuring the temperature near the outer wall of quartz amble 1 using thermocouples 5A, 5B, 5C, 5D, and 5E installed near the outer wall of quartz ampoule 1. Instead, a temperature measurement point was set at a location other than the vicinity of the outer wall of the quartz ampule 1, and preliminary experiments were conducted to determine the relationship between the newly provided temperature measurement point and the temperature near the outer wall of the quartz ampoule 1. The first temperature gradient (a'C / cm) and the second temperature gradient (te / cm) are controlled while measuring the temperature at that temperature measurement point. The single crystal growth may be performed by controlling.

According to the method for growing a single crystal according to the present invention, the second vertical temperature gradient (/ 3′C / cn) above the upper end of the ruffle causes the outer wall of the quartz ampule to correspond to the raw material melt. The single crystal grown from the melt surface was floated on the melt so that it did not contact the inner wall of the melt because it was larger than the first temperature gradient (cr'C / cin) in the vertical direction in the vicinity. As a result, the generation of new nuclei on the inner wall of the crucible is prevented, and a single crystal is easily obtained.

In addition, by controlling the vapor pressure by putting a volatile element in the reservoir, the applied vapor pressure can be maintained at an appropriate level without dispersing, and decomposition and raw materials on the surface of the grown single crystal can be maintained. Since evaporation from the melt is more effectively suppressed, lineage is reduced, large precipitates are prevented from being generated, and the quality of the single crystal is improved.

Furthermore, by using a PBN crucible having thermal conductivity anisotropy, the amount of heat applied to the lower portion of the crucible can easily be transferred to the upper portion of the side wall of the crucible, and the amount of heat dissipated in the horizontal direction can be reduced. It is extremely effective in keeping the inside wall above the melting point during crystal growth.

Furthermore, 'the first temperature gradient (a'C / cm) is 5 1 / D2~ 102 / D2'C / CB, more preferably ^{58 / D 2 - 83 / D} 2' if CZCB, melt In addition to stabilizing nucleation and preventing the nucleus from disappearing due to convection, the heat supply to the lower side of the crucible is maintained at an appropriate level. Is maintained above the melting point, so that a single crystal is easily obtained.

In particular, as a heating furnace, at least a first heating means for controlling the first temperature gradient (a'C / cn) and a second heating means for controlling the second temperature gradient (/ S'CZcni) A second heating means, a third heating means for heating the reservoir, a fourth heating means and a fifth heating means for suppressing the influence of disturbance, a first heating means and a third heating means. By using a multi-stage heating furnace having a sixth heating means for suppressing mutual influence with the second heating means, the first temperature gradient (a'CZciii) and the second temperature gradient (/ S ' The controllability of CZcia) is extremely improved, and the effect of dramatically improving the yield of single crystal substrates can be obtained. When growing a single crystal of CdZnTe or CdTe, the temperature of the reservoir If it is 770-830 ° C, the precipitate in the grown crystal is a small one with a diameter of at most about 10m, and if it is 790-820 ° C, The precipitates are very small, not exceeding a diameter of 5 m at the maximum, so that single crystals of very good quality are obtained.

As described above, the present invention has an effect that a single crystal having a larger diameter and a larger diameter can be manufactured with higher yield. Industrial applicability

As described above, the present invention is most effective when used for producing a compound semiconductor single crystal, particularly for producing a compound semiconductor single crystal by the VGF method while controlling the vapor pressure.

Claims

. The scope of the claims

1. A single substance or a compound made of at least one kind of volatile element among the constituent elements of the compound semiconductor is put into the reservoir part of the quartz amble having a reservoir part, and the raw material of the compound semiconductor is put in the quartz amble. After placing the crucible made of PBN and vacuum-sealing the quartz ampule, the quartz amble is heated in a heating furnace to melt the raw material, and the reservoir is heated to a predetermined temperature. Then, the vapor pressure of the element, which is easily volatilized in the reservoir portion, is applied to the quartz amble to control the vapor pressure, and the first temperature in the vertical direction near the outer wall of the quartz ampule corresponding to the melted raw material melt. While controlling the temperature distribution in the heating furnace, the temperature in the heating furnace is controlled so that the gradient is smaller than the second temperature gradient in the vertical direction above the upper end of the loop. When the compound semiconductor single crystal is grown downward from the surface of the raw material melt and the diameter of the single crystal to be grown is Den, the first temperature gradient is 51 / D2 ~ 102 / D2'CZcm, more preferably 58 / D2 ~ 8, while the cooling rate of the furnace temperature is R'C / hr, the thermal conductivity of the crystal is lkcal / cin'hr'K, When the specific gravity of the crystal is / og cn ³ and the latent heat of fusion of the crystal is Lkcal / noK ', the formula quantity of the crystal is n gZno 1, the following formula:

X = "(R / λ n L)

Wherein the second temperature gradient is 1.06 to 1.72X / cffl, more preferably 1.19X to 1.46X * C / CB. Single crystal growth method.

2. As the heating furnace, at least a first heating means disposed at a position corresponding to the crucible and controlling the first temperature gradient, and disposed above the first heating means. A second heating means for controlling the second temperature gradient, a third heating means disposed below the first heating means for heating the reservoir, and a second heating means for controlling the second temperature gradient. Fourth heating means and fifth heating means which are respectively disposed above the heating means and below the third heating means to suppress the influence of disturbance on the first temperature gradient and the second temperature gradient. Between the first heating means and the third heating means The unit according to claim 1, wherein a heating furnace provided with a sixth heating means disposed to suppress mutual influence between the first heating means and the third heating means is used. Crystal growth method.

3. The method for growing a single crystal according to claim 1, wherein the single crystal of the compound semiconductor is CdZnTe or CdTe.

4. The method of growing a single crystal according to claim 3, wherein the temperature of the reservoir is preferably 770 to 830, and more preferably 790 to 820'C.